when they go to another team. IMO a lot goes into the way they are used as well as who they are lined up with. Just like when getting a FA from another team and plugging them into the RAMS....sometimes the mesh just doesn't come about.....I remember "Road Grader" White from the jets I think, massive blocker came here and flopped.....same with several MLB we went through after Fletcher went.
There are also players who kinda do a 1 hit wonder deal as well......IMO it's hard to compare a player when going elsewhere to how they did here....a lot goes into that players game, not just his skills alone that makes or breaks it.....unless you are of the ultra rare breed.